Dual-Surface Optical Filter for Hα Transmission and Infrared Blocking
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Solution Overview
Problem
Existing optical filters in cameras, particularly those used for astrophotography, struggle with infrared light leakage causing ghosting and flare due to insufficient infrared blocking capabilities when infrared absorption glass is removed, leading to reduced image quality, especially in low-light conditions.
Innovation Solution
Implementing a dual-layer optical filter configuration with dielectric multilayer films on both surfaces of the optical filter, where each layer has distinct cut wavelengths to effectively block infrared light, preventing multiple reflections and ghosting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If infrared absorption glass is removed from the optical filter to increase Hα line transmittance for astrophotography, then the transmittance of Hα line light is significantly increased, but the capability of blocking infrared light is reduced, causing ghosting and flare in captured images
Solution Approach 1:
The optical filter is segmented into multiple functional layers: a first dielectric multilayer film on the first surface with a first cut wavelength, and a second dielectric multilayer film on the second surface with a second cut wavelength. This segmentation allows each layer to handle different aspects of light filtering, achieving both high Hα line transmittance and effective infrared blocking without ghosting.
Solution Approach 2:
Different regions of the optical filter have different optical properties tailored to specific functions. The first dielectric multilayer film is optimized for Hα line transmission with its cut wavelength set above 656.3 nm, while the second dielectric multilayer film is optimized for infrared blocking with its cut wavelength set below the first. This local differentiation of optical characteristics resolves the contradiction between transmitting Hα light and blocking infrared light.
2Object-affected harmful factors
If a single UV-IR blocking coat is used to block infrared light, then infrared blocking capability is improved, but multiple reflections occur between vapor-deposited surfaces causing red ghost light near bright spots
Solution Approach 1:
The single UV-IR blocking coat is divided into two separate dielectric multilayer films positioned on opposite surfaces of the optical filter. The first film's cut wavelength is set higher than 656.3 nm to allow Hα line transmission, while the second film's cut wavelength is set lower to block infrared light. This segmentation eliminates the multiple reflection problem by separating the blocking functions into distinct layers with non-overlapping reflection bands.
Solution Approach 2:
The cut wavelengths of the two dielectric multilayer films are specifically parameterized to resolve the contradiction. The first cut wavelength is set above 656.3 nm (e.g., 680-780 nm) to transmit Hα line light, while the second cut wavelength is set below 656.3 nm (e.g., 630-680 nm) to block infrared light. This parameter differentiation ensures that reflections from the two films do not overlap, preventing ghost light while maintaining effective infrared blocking.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The dual-layer filter design significantly reduces ghosting and flare, maintaining high image quality by effectively blocking infrared light across a wide range, even in low-light conditions.
Implementation Method 1
a first optical film that reflects at least one of light in a longer wavelength band than a first wavelength and light in a shorter wavelength band than a second wavelength shorter than the first wavelength is formed on a first surface of the at least one optical member
Implementation Method 2
an optical filter having an optical low-pass function and an infrared absorption function is arranged in a front surface of an image sensor
Data Source
AI summary
An optical filter comprises at least one optical member that transmits light, wherein a first optical film that reflects at least one of light in a longer wavelength band than a first wavelength and light in a shorter wavelength band than a second wavelength is formed on a first surface, and a second optical film that reflects at least one of light in a longer wavelength band than a third wavelength and light in a shorter wavelength band than a fourth wavelength is formed on a second surface, the second surface being different from the first surface, and the first wavelength and the third wavelength are different from each other by a first predetermined amount, and the second wavelength and the fourth wavelength are different from each other by a second predetermined amount.